MYB20, an R2R3-type MYB transcription factor, negatively regulates salt and cold stress tolerance in pears

As one of the largest families of transcription factors (TFs) in plants, MYB TFs play an important role in regulation responses to environmental stressors. However, the precise function of MYB TFs in abiotic stress responses in pear is not yet well-understood. Here, we identify an R2R3-type MYB TF, PpcMYB20, in pear that is significantly induced by multiple abiotic stresses, as evidenced by elevated expression after NaCl, cold, PEG6000, and abscisic acid (ABA) treatments. Comprehensive functional validation indicates that PpcMYB20 functions as a negative regulator in multiple abiotic stress responses across various plant families. Up-regulated expression of PpcMYB20 significantly represses the growth of pear calli cultured under salt stress conditions. Overexpression of PpcMYB20 in Arabidopsis increased the sensitivity to salt stress, resulting in decreased seed germination rate, lower survival, less chlorophyll content and increased reactive oxygen species (ROS) accumulation. Likewise, ectopic expression of PpcMYB20 also led to diminished salt tolerance in transgenic tomato plants. More interestingly, pear calli overexpressing PpcMYB20 display a salt-sensitive phenotype after chilling treatment. Transgenic Arabidopsis and tomato plants also exhibit a reduced capacity for cold tolerance. Taken together, these findings suggest that PpcMYB20 is a multiple stress-inducible R2R3-type MYB TF that plays a negative regulatory role of salt and cold tolerance in pear. This will provide more options for pear resistance breeding research and promote the development process of pear abiotic stress field.